Data AcQuisition And Real-Time AnalysisScope - Spectrum - Spectrogram - Signal Generator
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Trigger Single-Frame Toggle
When you activate the Single button, the Trigger buttons (just above it in the Trigger dialog, and also on the Daqarta toolbar) change to "Trig Arm" and are shown depressed. But as soon as the first trigger event occurs and a frame is shown, the Trig Arm buttons pop out and the display enters Pause mode. The Single button stays active; hitting Trig Arm (or ALT+T) re-arms the system to wait for the next frame. As long as Single is active, hitting unPause will do the same thing.
Single-frame operation is useful for capturing transient signals, especially those with long durations. For example, suppose the signal is an intermittent tone burst, and you want to observe the beginning portion. You can set the trigger Slope and Level to trigger on the initial rise of the burst, and an ordinary trigger will indeed happen at that time, showing the start of the burst on the screen. The problem is that as the burst tone continues, each additional cycle can cause a trigger. So the initial trace will quickly be overwritten by later portions of the ongoing burst.
In Single-frame mode, however, the trace is Paused after the initial frame, freezing the display of the desired early portion of the burst.
Also, if Pause is already active when you first toggle Single on, you will have to manually unPause to start the trigger scan, even though Trig Arm is set. Once the trigger is found and the display is updated and Paused, simply hitting Trig Arm will unPause and perform additional Single frame acquisitions.
Trigger Delay can be used with Single to see what happened just before the start of the burst (by setting a negative Delay), or to see a specific portion later in the burst (using a positive Delay).
Notice that for this method to work as described, you need to arm the Trigger during the interval between bursts, so that the next trigger event seen by the trigger logic is the start of a burst. But since the display is not continuously updated, you can't tell when the burst is active or not... you might hit Trig Arm during the ongoing portion and the next cycle will start the capture mid-burst. So you might have to hit Trig Arm blindly a few times until you get it right. Obviously, you can expect to need more attempts if the time between bursts is short compared to the burst duration.
Thus, it is helpful if you can arrange to have some control over the timing of the signal, or at least to have some way to know when the signal is silent versus ongoing. A speaker or other relevant monitor may be used. If there are fairly long times between bursts, you can leave Trigger and Single off and watch the trace until you see that a burst has ended, then quickly hit Single.
Of course, if you have control over the signal, you can just stop it, hit Single, and then start the signal.
The ideal situation for capturing transients is when the signal you wish to observe is a response to a stimulus from the Daqarta Generator. In that case, you probably don't need Single at all, since you can use Gen Sync to sync to the Burst start or other Generator sync period.
If you have a file that contains infrequent bursts of desired responses separated by long intervals of uninteresting low-level background signals or noise, you can use Single to skip over the unwanted portions to show just the desired regions. The desired response must be enough larger than the background that you can set a reliable trigger level.
Sometimes you may be interested in low-level events that come just before or after a large burst. In that case, you can still set the trigger level for the burst, but after Single locates it and Pauses, you can use the normal DDisk scroll keys to view earlier or later portions.
Alternatively, if you know that the desired portion will always be within a fixed interval before or after the burst, you can set Trigger Delay to show just that portion each time you hit Trig Arm to activate Single.
In Spectrogram or Pitch Track (Sgram/PT) modes with Single active, each time the Trig Arm button is hit the display is cleared. Then, after a trigger event is detected, Trig Arm is toggled off and a full-screen spectrogram is obtained before entering Pause. Since there is no further triggering action, the individual spectra in the rest of the spectrogram are simply taken as fast as possible, as determined by the Trace Update Interval.
When reading DDisk files, the same general behavior occurs. The main difference is that once the initial trigger is found, the spectra for rest of the spectrogram are spaced according to the DDisk Read Step Size, unrelated to the Trace Update Interval. Temporal resolution is determined by Read Step Size, while speed of spectrogram creation is determined only by system processing speed.
TrigSngl=1 activates Trigger Single mode, TrigSngl=0 turns it off, and TrigSngl=x toggles between on and off.
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